image =	lightnessImg (inColorImg)
image =	lightnessImg (inColorImg,lightnessType)

Detailed Description

lightness computation for an input color image

The algorithm converts a color image to a grey level one according to one of the three possible types: Average, Lightness or Luminance. The default value is Average.

Assuming that $InColorImg[i, c]$ is the $i^{th}$ pixel in the channel $c$ , we can define the three different ways to calculate the lightness.

For the Average type, the output image values are given by:

$OutLightImg[i] = \frac{\sum_{c}{InColorImg[i, c]}} {NbChannels}$

For the Lightness type, the output image values are given by:

$OutLightImg[i] = \frac{\max_{c}(InColorImg[i, c]) + \min_{c}(InColorImg[i, c])} {2}$

The Luminance type can only be calculated for images with three channels and is assumed to be RGB. The output image values are given by:

$OutLightImg[i] = 0.21 InColorImg[i, 0] + 0.72 InColorImg[i, 1] + 0.07 InColorImg[i, 2]$

Input and output images must have same size (but color size).

Here is an example of an average ligthness operation applied to a 8-bits RGB color image:

Example of Python code :

Example imports

import PyIPSDK

import PyIPSDK.IPSDKIPLColor as color

Code Example

    # opening of input image
    geometryRgb = PyIPSDK.geometryRgb2d(PyIPSDK.eImageBufferType.eIBT_UInt8, 510, 509)
    inImg = PyIPSDK.loadRawImageFile(inputImgPath,  geometryRgb)
    
    # lightness computation
    outImg = color.lightnessImg(inImg)

Example of C++ code :

Example informations

Header file

#include <IPSDKIPL/IPSDKIPLColor/Processor/LightnessImg/LightnessImg.h>

Code Example

        // opening input image
        ImagePtr pInColorImg = loadTiffImageFile(inputImgPath);
        
        // compute lightness on input image
        ImagePtr pOutLightImg = lightnessImg(pInColorImg, lightnessType);